The invention relates to a service water heating unit according to the preamble of claim 1.
Service water heating units of this type are used in heating installations to heat service water which is then supplied, for example, to wash basins, showers and bathtubs as hot water. For example, the heating may take place in a service water storage container or else via a heat exchanger. Such a heat exchanger comprises two flow paths: one for the heating medium, i.e. normally the water which is heated by the heating boiler and flows through the heating installation, and a second flow path through which the service water to be heated is conveyed.
Known heat exchangers have either a co-current arrangement, in which the flow paths for the service water and the heating medium are oriented in the same direction, or else a countercurrent arrangement, in which the directions of flow of heating medium and service water are oriented in opposite directions. With the co-current arrangement there is the drawback that the outlet side for the heating medium and the service water are located at the same end of the heat exchanger and therefore the maximum temperature for the service water to be heated can, at most, correspond to the outlet temperature of the cooled heating medium from the heat exchanger. In practice, the temperature will lie below this. This means, very high temperatures of the heating medium on the inlet side of the heat exchanger are necessary in order to achieve high service water temperatures. With the countercurrent arrangement higher outlet temperatures for the service water can be reached since the outlet of the heated service water and the inlet of the heating medium are located on the same side of the heat exchanger. This means, the service water is heated in the heat exchanger by the incoming heating medium, i.e. the as yet uncooled heating medium, in the vicinity of the outlet side. However, this arrangement in turn poses the drawback that, in particular with low service water volume flow rates, the outlet temperature of the service water may be too high. In addition to a risk of scalding, an excessively high service water temperature also poses the drawback that it may lead to increased limescale in pipes and fittings.
In view of this problem, the object of the invention is to provide an improved service water heating unit which ensures a sufficient heating of the service water, but can also reliably prevent excessively high temperatures of the service water.
This object is achieved by a service water heating unit having the features disclosed in claim 1. Preferred embodiments will emerge from the dependent claims, the description below and the accompanying drawings.